The present invention relates to a damper for dampening rotational movements of a vane type angle of attack sensor, which will insure that the vane will not invert and also will reduce vane dither and xe2x80x9cover shootxe2x80x9d to allow a stable measurement of angle of attack. The damper includes a rotor in a housing chamber having a clearance space filled with an electrorheological or magneto-rheological fluid the viscosity of which is varied to control the damping of movement of the rotor.
Existing vane type angle of attack sensors include dampers that have a fluid filled housing chamber with a rotor in the housing chamber, but which utilize a fluid that has a known viscosity at selected temperatures. The fluid typically is heated to a nominally constant temperature to attempt to avoid changes in viscosity due to differences in ambient temperatures that are encountered during operation of an aircraft.
In conventional systems, a vane that is optimally damped for high mach number or high air speed, will be damped more than is needed at a lower speed. This causes a lower response time at lower speeds. If a vane is optimally damped for a lower speed, the response time at higher speeds suffers. It has been found that in certain instances, the standard damping fluid is not adequately controllable for maintaining suitable damping across a wide range of operational parameters, such as aircraft velocity and ambient temperature.
The present invention utilizes a rotor attached to the shaft of a rotating vane angle of attack sensor, which is in a housing and is surrounded by an electrorheological or magnetorheological fluid. The fluid viscosity is controlled and changed in response to a signal, generally an electrical signal, that will vary either the voltage across the electrorheological fluid or the strength of a magnetic field affecting a magnetorheological fluid. The control signals are based upon outside parameters such as aircraft velocity (mach number), turbulence, the actual aircraft configuration, altitude, angle of attack, and rate of change of angle of attack. The various factors are called aircraft operational parameters.
Continuously adjusting the damping to the proper level based on current flight conditions, including the aircraft operational parameters mentioned, allows the vane to perform optimally at such flight conditions. Variations in viscosity of the signal responsive fluid can be accomplished by providing a variable electrical signal through a control circuit that will have an input from the air data computer indicating the level of damping desired in real time. The change in viscosity can be on the order of microseconds so that real time control is achieved.